A sodium-led bicarbonate spring — the classic 'juso-sen' style, soft and rounded on the skin. Hypotonic, neutral pH, sitting in the Japanese 'beauty-water' family. Metasilicic acid runs to 108.6 mg/kg, leaving a thin silica film that makes skin feel smoother afterwards. Free CO₂ at 284 mg/kg arrives as an aromatic gas, paired with a faint mineral tang and the merest whisper of H₂S at the wellhead.
Good for
Smooth skin
Bicarbonate and alkalinity gently lift dead keratin while silica hydrates, leaving skin smooth. This is the basis of the beautifying-water (bijin-no-yu 美人の湯) reputation.
dry, rough skin
Recovery
Warmth and buoyancy lower stress markers and improve sleep; habitual bathing is linked to lower rates of depression.
fatigue, stress
Take care
From a certificate analyzed in 2020.
- Active stage of any illness (especially with fever), active tuberculosis, advanced malignant tumor, severe anemia or other marked physical weakness, severe heart or lung disease causing shortness of breath on slight exertion, severe kidney disease with edema, gastrointestinal bleeding, visible bleeding, acute exacerbation of a chronic illness
Full composition
The bar is each ion's share of charge (mval%) within its group; over 20% names the spring. Gases, silica and trace metals are measured by mass only.
- Sodiumsalt's cation — pairs with chloride to make the water saltyNa⁺245mgP58 national85%
- Calciumsettling and calming; can leave a white mineral bloomCa²⁺14.7mgP31 national6%
- Magnesiummild; a laxative if you drink itMg²⁺7.6mgP58 national5%
- Potassiumminor; matters for drinking limitsK⁺13.8mgP52 national3%
- AmmoniumNH₄⁺0.80mgP60 national0.3%
- LithiumLi⁺0.20mgP37 national0.2%
- BariumBa²⁺1.1mgP90 national0.2%
- AluminumAl³⁺0.10mgP56 national0.1%
- StrontiumSr²⁺0.50mgP68 national0.1%
- ManganeseMn²⁺0.20mgP47 national0.1%
- Bicarbonate"soda" — softens skin, leaves it smoothHCO₃⁻635mgP82 national82%
- Chloridetable-salt anion — coats the skin and holds heat inCl⁻71.8mgP31 national16%
- Sulfate"gypsum / Glauber's salt" — vessels and wound healingSO₄²⁻8.1mgP19 national1%
- FluorideF⁻0.20mgP16 national0.1%
- Iodideyellows in air; helps blood lipidsI⁻0.10mgP34 national
- Hydrogen phosphateHPO₄²⁻0.05mgP21 national
- Thiosulfateoxidized sulfurS₂O₃²⁻0.03mgP31 national
- Bromidetrace, sea-originBr⁻0.0040mgP6 national
- Metasilicic acidmetasilicic acid — a natural moisturizer for silky skinH₂SiO₃109mgP57 national
- Metaboric acidmetaboric acid — mildly antibacterialHBO₂12.9mgP62 national
- Free carbon dioxidefizz — widens blood vessels (strong above 1000 mg/kg)CO₂284mgP92 national
- Free hydrogen sulfide"egg" smell — opens vessels, antibacterialH₂S0.04mgP51 national
- CadmiumCd< —mg
- ChromiumCr< —mg
- Mercurytoxic trace — part of the drinking-safety checkHg< —mg
- LeadPb< —mg
Measured at the source
On the certificate
From a certificate analyzed in 2020.
- Chronic muscle or joint pain or stiffness (the chronic phase of rheumatoid arthritis, osteoarthritis, lower back pain, neuralgia, frozen shoulder, bruises, sprains and the like), muscle stiffness associated with motor paralysis, cold sensitivity, peripheral circulation disorders, reduced gastrointestinal function (bloating), mild hypertension, impaired glucose tolerance (diabetes), mild hypercholesterolemia, mild asthma or emphysema, autonomic nervous system instability, stress-related symptoms (sleep disorders, depressed mood), convalescence, fatigue recovery, general health improvement
- Cuts, peripheral circulation disorders, cold sensitivity, dry skin
Evidence
- Maeda M. 温泉の医学的効果とその科学的根拠. J. Hot Spring Science 70:197–207, 2021.
- Naito Y et al. A Hot-Spring Water Improves Inflammatory Conditions in an Atopic Dermatitis Model. Biomedicines 13(11):2707, 2025.
- Li H et al. Bicarbonate Ionized Water Bathing Enhances Natural Killer Cell Activity. Scientific Reports 14:51851, 2024.
- Takeda M et al. Hot spring bathing practices have a positive effect on mental health in Japan. Heliyon 9(9):e19631, 2023.